This invention relates to personal care absorbent articles employing nonwoven web materials comprising polymeric fibers having a reduced amount of polymer compared to conventional solid polymeric fibers of corresponding dimensions. More particularly, this invention relates to polymeric fibers in which a gaseous or liquid fluid is injected into the core or center of the fibers during production of the fibers, which liquid or gaseous fluid remains in the interior of the fibers, and a method for producing such polymeric fibers. Polymeric fibers having high or low density cores and trapped liquid cores can be produced in accordance with the disclosed method. Improved characteristics of these fibers include more resilient crimp and improved insulation properties. Nonwoven web materials comprising such fibers are suitable for use in personal care absorbent articles such as diapers, incontinence garments, training pants, feminine care products such as sanitary napkins and pads, and the like.
Nonwoven materials are defined as materials having a structure of individual fibers or threads which are interlaid, but not in a regular or identifiable manner, as in a knitted fabric. Nonwoven webs can be formed by many processes such as, for example, meltblowing processes, spunbonding processes, and bonded carded web processes. Typically, the fibers from these processes are deposited onto a forming wire or belt for formation of the web.
Nonwoven materials and laminates comprising nonwoven materials are widely used as components of absorbent articles such as disposable diapers, feminine hygiene products including sanitary pads and tampons, incontinence garments, disposable medical garments and the like, and much effort has been made to improve the effectiveness and functionality of these articles. These articles generally include a liquid absorbent material backed by a liquid-impervious barrier sheet. To enhance the sense of comfort, the absorbent material has a facing of a material which masks at least the body-facing surface of the product. The purpose of this cover or liner material is to help structurally contain the absorbent material and to protect the wearer from continuous direct contact with moisture from previously wetted absorbent material. The cover material is typically a relatively low basis weight nonwoven fabric. Improved product performance has been obtained in these products through the incorporation of a surge management material disposed between this cover material and the absorbent material. (See U.S. Pat. No. 5,429,629.) The surge management material is made from a relatively high basis weight, low density, that is thick, nonwoven web material. The cover material must, therefore, be permeable to liquids on the side of the product that is placed against the body, actively promoting the immediate transfer of each liquid application or insult through the surge management material and into the absorbent pad. It is also necessary that the surge management material initially hold the liquid passed through the cover material and then give up said liquid to the absorbent material.
One characteristic of a liner material which affects the fluid intake characteristics of the material is the amount of void volume within the material. In particular, by increasing the amount of void volume, the fluid intake characteristics, that is the ability of the liner material to initiate fluid intake, is improved. For nonwoven liners, void volume, or pore size, is typically increased by increasing the fiber diameter which, in turn, translates into a higher amount of polymer per unit length of fibers making up the liner material. However, increasing the fiber diameter of solid fibers by conventional means results in an increase in the amount of polymer required to produce the fibers which make up the liner material.
In addition to the benefits derived from increasing the fiber diameter as discussed hereinabove, there are also benefits derived from increasing the surface area of the fibers comprising a nonwoven web material. For example, increasing the surface area of the fibers enables the application of a greater amount of topical surfactant to the fibers, which, in turn, may also enhance the fluid uptake ability of the nonwoven web. To increase the surface area of a solid fiber by conventional means, it is typically necessary, as in the case of increasing fiber diameter, to increase the polymer amount per unit length of fiber.
Accordingly, it is one object of this invention to provide a nonwoven material having fibers with a reduced polymer weight per unit length of fiber compared to conventionally formed solid fibers having corresponding dimensions.
It is another object of this invention to provide a personal care absorbent article employing such nonwoven materials.
It is another object of this invention to provide a method for increasing the dimensional characteristics, such as fiber diameter and surface area, of a polymeric fiber suitable for use in nonwoven materials without increasing the amount of polymer utilized per unit length of fiber.
It is another object of this invention to provide a method for increasing the dimensional characteristics, such as fiber diameter and surface area, of a polymeric fiber suitable for use in nonwoven materials while decreasing the amount of polymer utilized per unit length of fiber compared to fibers produced by conventional means having corresponding dimensional characteristics.
It is yet another object of this invention to provide nonwoven materials having improved, more resilient crimp and improved insulation properties over conventional nonwoven materials.
These and other objects are addressed by a personal care absorbent article comprising a nonwoven material comprising a plurality of polymeric fibers having a fiber interior comprising at least one of a liquid fluid and a gaseous fluid. In accordance with one embodiment of this invention, the gaseous and/or liquid fluid is dispersed, for example as a plurality of tiny bubbles, throughout at least a portion of the fiber interior. The polymeric fibers may be spunbond fibers, meltblown fibers, bicomponent fibers, biconstituent fibers, bonded carded fibers and combinations thereof. In accordance with one embodiment of this invention, at least a portion of the polymeric fibers are crimped. Personal care absorbent articles in which these fibers may be used include, but are not limited to, disposable diapers, incontinence garments, training pants, feminine care products including sanitary pads and tampons, wipes, surgical gowns and wound dressings.
Polymeric fibers for use in nonwoven materials for personal care absorbent articles in accordance with this invention are produced by a method comprising the steps of introducing at least one polymer suitable for forming polymeric fibers into an extruder and heating said polymer to an extrusion temperature, forming a molten polymer, introducing a blowing agent in the form of a liquid and/or gaseous fluid into the molten polymer, and extruding the polymer, resulting in the formation of a plurality of polymeric fibers having a reduced amount of polymer per unit of length of fiber compared to conventional solid polymeric fibers having corresponding fiber dimensional characteristics. In accordance with one embodiment of this invention, the blowing agent is introduced into the at least one polymer prior to extrusion, resulting in the blowing agent being dispersed within at least a portion of the extruded polymeric fibers. In accordance with one embodiment of this invention, the extruded polymeric fibers are monocomponent or bicomponent fibers wherein the blowing agent is introduced substantially only into one of the polymer streams forming the extruded bicomponent fibers. For example, for a bicomponent fiber having a sheath-core configuration, the blowing agent may be disposed substantially only in the core portion of the bicomponent fiber. Alternatively, each component of the bicomponent fiber may include a different blowing agent dispersed throughout the component. In accordance with yet a further embodiment of this invention, the polymeric fibers are biconstituent fibers wherein the blowing agent is dispersed within one polymeric component of the biconstituent fibers.
It will be apparent to those skilled in the art that the polymeric fibers of this invention, while not necessarily having a reduced weight per unit of fiber volume or length (the weight being a function in part of the blowing agent employed), will, nevertheless, have a reduced amount of polymer per unit of volume compared to polymeric fibers of comparable dimensions without any blowing agent. This is due to the displacement of a portion of the otherwise polymeric volume of the fibers by the blowing agent.
It also will be apparent to those skilled in the art that the type of blowing agent(s) used as well as the manner in which it is introduced into the fiber will impact the end product fiber characteristics. Thus, the type of blowing agent employed may be predicated upon imparting a particular characteristic to the fibers to satisfy the requirements of the personal care absorbent article in which it is used. A center-filled fiber can be produced having high or low density cores, liquid trapped cores, improved, more resilient crimp and improved insulation properties. This, in turn, will affect the properties of nonwoven materials produced using these fibers, such as basis weight, void volume, etc. Suitable blowing agents are gaseous or liquid fluids which are unreactive with the fiber polymer. Gaseous fluids, such as high pressure air and nitrogen, are preferred.